Undo commit 3b5fe88f43af91f09cbe16e68bd627baadedabef

Changing the underlying image to ubuntu:14.04.2 broke the GUI.  Reverting back until we can do more testing and fix the resulting issues.
diff --git a/containers/xos/Dockerfile b/containers/xos/Dockerfile
index 7e9db23..0fd7565 100644
--- a/containers/xos/Dockerfile
+++ b/containers/xos/Dockerfile
@@ -1,4 +1,4 @@
-FROM       ubuntu:14.04.2
+FROM       python:2.7.11
 
 # XXX Workaround for docker bug:
 # https://github.com/docker/docker/issues/6345